Iron-Nickel-Cobalt Alloy

ABSTRACT

Use of an iron-nickel-cobalt alloy in CFC mould construction comprising (in % by mass) Ni from 30 to 35%, Co from 3 to 6%, Al from 0.001 to 0.1%, Mn from 0.005 to 0.5%, Si from 0.005 to 0.5%, C max. 0.1%, balance Fe and constituents resulting from production, with the alloy having a mean coefficient of thermal expansion in the temperature range from 20 to 200 DEG C of &lt;2.0 OE10&lt;−6&gt;/K.

The invention relates to the use of an iron-nickel-cobalt alloy.

Increasingly, components are being produced from carbon fiber-reinforced composites (CFC), even those for products with safety considerations, such as in aircraft manufacture. For producing such components, implements (molds) are needed in which the viscous resin-carbon fiber layer is cured at a temperature of approx. 180° C. In the so-called RTM (resin transfer molding) process, carbon fiber textiles are added to the mold, the mold is evacuated, and then the resin is injected into the mold. After curing at approx. 180° C., the component is removed from the implement. Materials used for these molds are either C steels or an alloy with a low coefficient of expansion (iron with 36% nickel, Ni36) that typically has a mean thermal expansion coefficient between 1.6 and 2.5×10⁻⁶ K⁻¹.

The use of these RTM molds is associated with difficulties and significant complexity because after it is cured the component is difficult to release from the mold and in addition the component must undergo complex subsequent processing so that it can satisfy its functional demands.

The underlying object of the invention is therefore to provide an alloy for these molds, with which alloy the aforesaid difficulties can be overcome simply.

This object is attained by using an iron-nickel-cobalt alloy in the CFC mold having (in % by weight):

Ni 30 to 35% Co 3 to 6% Al 0.001 to 0.1% Mn 0.005 to 0.5% Si 0.005 to 0.5% C Max. 0.1% remainder Fe and constituents resulting from the production process, the alloy having a mean thermal expansion coefficient of <2.0×10⁻⁶/K in the temperature range from 20 to 200° C.

Advantageous refinements of the inventive subject-matter can be found in the subordinate claims.

Depending on the application area, the Ni content can be adjusted ranging from 32 to 34.5%, where needed even 32.5 to 33.5%.

One preferred alloy is distinguished by the following composition (in % by weight):

Ni 32.5 to 34.5% Co >3.0 to 5.5% Al 0.001 to 0.5% Mn 0.005 to 0.1% Si 0.005 to 0.1% C 0.005 to 0.05% remainder Fe and constituents resulting from the production process, the alloy having a mean thermal expansion coefficient of <1.5×10⁻⁶/K in the temperature range from 20 to 200° C.

The following elements with the given maximum contents can advantageously be provided for accompanying elements in the alloy to be used:

Cr max. 0.1% Mo max. 0.1% Cu max. 0.1% Ti max. 0.1% Mg max. 0.005% B max. 0.005% N max. 0.006% O max. 0.003% S max. 0.005% P max. 0.008% Ca max. 0.005% Zr max. 0.05%

Another alloy that can be used advantageously is distinguished by the following chemical composition (in % by weight):

Ni 32.5 to 34.5% Co >3.5 to <4.5% Mo max. 0.05% Cr max. 0.05% C max. 0.009% Mn max. 0.04% Si max. 0.03% S max. 0.003% N max. 0.004% Ti max. 0.01% Cu max. 0.05% P max. 0.005% Al 0.001 to 0.05% Mg max. 0.0008% Ca max. 0.0001% Zr max. 0.03% O max. 0.006% remainder Fe and constituents resulting from the production process, the alloy having a mean thermal expansion coefficient of <1.3×10⁻⁶/K in the temperature range from 20 to 200° C.

Advantageously, the molds are made as milled parts from heat-formed (forged or rolled) or cast mass material and then annealed. The alloy can also be used in the form of wire material, in particular as an added welding substance when producing the mold.

One preferred application for the alloy is found in aircraft manufacture, wherein it is possible to use the alloy as a molded component, in particular for producing CFC fittings using the RTM technology. Other aircraft components that are also embodied using the light-weight CFC construction can also be produced with components made of the suggested alloy.

Compared to alloys based on N±36 that have been used in the past, components can easily be removed from molds of this alloy, because the thermal shrinkage of the mold is lower after the curing process. Given a suitable design for the mold, the component can be removed such that it can perform its function without subsequent processing.

The simpler removal of the component from the mold will also increase the service life of the mold, because no sharp-edged tools have to be used in order to release the component from the mold.

Table 1 provides examples of chemical compositions for inventive iron-nickel-cobalt alloys (E1, E2, E3, E4, E5, E6) compared to other iron-nickel-cobalt alloys (T1, U1) that were investigated.

Element (%) E1 E2 E3 E4 E5 E6 T1 U1 C 0.002 0.47 0.002 0.008 0.002 0.036 0.004 0.002 S 0.0023 0.0009 0.0006 0.0015 0.0004 0.0011 0.0008 0.0025 N 0.001 0.001 0.001 0.001 0.001 Cr 0.02 0.01 <0.01 <0.01 <0.01 0.01 0.01 0.02 Ni 34.20 34.25 32.75 32.80 32.80 32.55 35.50 34.20 Mn <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.03 <0.01 Si 0.07 <0.01 <0.01 <0.01 <0.01 <0.01 0.04 0.11 Mo 0.01 0.02 0.01 0.01 0.05 0.09 Ti <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Cu 0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.05 0.01 P 0.002 0.002 0.002 0.002 0.002 0.002 0.002 0.003 Al 0.004 0.007 0.001 0.005 0.005 0.014 0.011 0.010 Mg 0.0004 0.0003 0.0003 0.0003 0.0002 0.0003 0.0006 0.0005 Ca 0.0004 <0.001 0.0006 0.0006 0.0007 <0.001 0.0002 0.0003 Co 3.1 3.1 3.38 3.9 4.45 4.9 1.44 2.3 Fe Remainder Remainder Remainder Remainder Remainder Remainder Remainder Remainder

Inventive alloys E1-E3 and E6 attain thermal expansion coefficients ranging from 1.5-<2.0×10⁻⁶/K in the 20-200° C. temperature range.

The inventive alloys E4 and E5 attain an even lower expansion coefficient of about 1.3×10⁻⁶/K in the 20 to 200° C. temperature range so that with the alloys E4 and E5 a combination of increased strength with simultaneously lower thermal expansion is attained. 

1. A method comprising fabricating a mold from materials comprising an iron-nickel-cobalt alloy and producing an object of carbon-fiber reinforced composite in the mold, the alloy comprising, in % by weight: Ni 30 to 35% Co 3 to 6% Al 0.001 to 0.1% Mn 0.005 to 0.5% Si 0.005 to 0.5% C max. 0.1%

remainder Fe and impurities, the alloy having a mean thermal expansion coefficient of <2.0×10⁻⁶/K in a temperature range from 20 to 200° C.
 2. Method in accordance with claim 1, wherein the Ni content of the alloy is 32.0 to 34.5%, in % by weight.
 3. Method in accordance with claim 1, wherein the Ni content of the alloy is 32.5 to 33.5%, in % by weight.
 4. Method in accordance with claim 1, wherein the alloy comprises in % by weight: Ni 32.5 to 34.5% Co >3.0 to 5.5% Al 0.001 to 0.5% Mn 0.005 to 0.1% Si 0.005 to 0.1% C 0.005 to 0.05%

remainder Fe and impurities, the alloy having a mean thermal expansion coefficient of <1.5×10⁻⁶/K in a temperature range from 20 to 200° C.
 5. Method in accordance with claim 1, wherein the alloy comprises the following maximum contents of the following elements, in % by weight: Cr max. 0.1% Mo max. 0.1% Cu max. 0.1% Ti max. 0.1% Mg max. 0.005% B max. 0.005% N max. 0.006% O max. 0.003% S max. 0.005% P max. 0.008% Ca max. 0.005% Zr max. 0.05%


6. A method, comprising fabricating a mold from materials comprising an iron-nickel-cobalt alloy and producing an object of carbon-fiber reinforced composite in the mold, the alloy comprising, in % by weight: Ni 32.5 to 34.5% Co >3.5 to <4.5% Mo max. 0.05% Cr max. 0.05% C max. 0.009% Mn max. 0.04% Si max. 0.03% S max. 0.003% N max. 0.004% Ti max. 0.01% Cu max. 0.05% P max. 0.005% Al 0.001 to 0.05% Mg max. 0.0008% Ca max. 0.0003% Zr max. 0.05% O max. 0.006%

remainder Fe and impurities, the alloy having a mean thermal expansion coefficient of <1.3×10⁻⁶/K in a temperature range from 20 to 200° C.
 7. Method in accordance with claim 1 or 4, wherein the alloy further comprises 0.001 to 0.1%, in % by weight, Nb.
 8. Method in accordance with claim 1 or 4, wherein the alloy from which the mold is fabricated comprises sheet material, strip material, or tube material.
 9. Method in accordance with claim 1 or 4, wherein the alloy from which the mold is fabricated comprises wire and the fabricating of the mold comprises welding with the wire comprised of the alloy.
 10. Method in accordance with claim 1 or 4, wherein the object comprises an aircraft part.
 11. Method in accordance with claim 1 or 4, wherein the alloy from which the mold is fabricated is in the form of forged stock.
 12. Method in accordance with claim 1 or 4, wherein the alloy from which the mold is fabricated is in the form of cast stock. 